The present invention relates to aircraft cabin pressure control and, more particularly, to a system and method for controlling the rate of change of pressure in an aircraft cabin to a substantially constant magnitude during the aircraft""s ascent.
For a given airspeed, an aircraft may consume less fuel at a higher altitude than it does at a lower altitude. In other words, an aircraft may be more efficient in flight at higher altitudes as compared to lower altitudes. Moreover, bad weather and turbulence can sometimes be avoided by flying above such weather or turbulence. Thus, because of these and other potential advantages, many aircraft are designed to fly at relatively high altitudes.
As the altitude of an aircraft increases, from its take-off altitude to its xe2x80x9ctop of climbxe2x80x9d or xe2x80x9ccruisexe2x80x9d altitude, the ambient atmospheric pressure outside of the aircraft decreases. Thus, unless otherwise controlled, air could leak out of the aircraft cabin causing it to decompress to an undesirably low pressure at high altitudes. If the pressure in the aircraft cabin is too low, the aircraft passengers may suffer hypoxia, which is a deficiency of oxygen concentration in human tissue. The response to hypoxia may vary from person to person, but its effects generally include drowsiness, mental fatigue, headache, nausea, euphoria, and diminished mental capacity.
Aircraft cabin pressure is often referred to in terms of xe2x80x9ccabin pressure altitude,xe2x80x9d which refers to the normal atmospheric pressure existing at a certain altitude. Studies have shown that the symptoms of hypoxia may become noticeable when the cabin pressure altitude is above the equivalent of the atmospheric pressure one would experience outside at 8,000 feet. Thus, many aircraft are equipped with a cabin pressure control system to, among other things, maintain the cabin pressure altitude to within a relatively comfortable range (e.g., at or below approximately 8,000 feet) and allow gradual changes in the cabin pressure altitude to minimize passenger discomfort.
Aircraft cabin pressure control systems are robustly designed and manufactured, and are operationally safe. Nonetheless, these systems suffer certain drawbacks. For example, some systems implement a control scheme that, in some instances, allows undesirably high cabin pressure rates of change during aircraft ascent. In addition, some cabin pressure control systems implement control schemes in which the cabin pressure rate of change is proportional to the aircraft ascent rate. Because aircraft ascent rate may vary, cabin pressure rate of change may undesirably vary during the aircraft ascent. Both of these situations can be disconcerting to the aircraft passengers and/or crew.
Hence, there is a need for a cabin pressure control system that implements a control scheme that overcomes one or more of the above-noted drawbacks. Namely, a cabin pressure control system and method that does not change cabin pressure at undesirably high rates during aircraft ascent, and/or does not vary cabin pressure rate of change during aircraft ascent, even if aircraft ascent rate varies. The present invention addresses one or more of these needs.
The present invention provides a cabin pressure control system and method that provides a substantially fixed cabin pressure rate of change magnitude during aircraft ascent.
In one embodiment, and by way of example only, a method of controlling aircraft cabin altitude during aircraft ascent to an aircraft cruise altitude includes determining a target cabin altitude, which corresponds to a desired cabin altitude at the aircraft cruise altitude. Aircraft cabin altitude rate of change is automatically controlled to at least one of a first and a second substantially constant value at least until the target altitude is attained.
In another exemplary embodiment, an aircraft cabin pressure control system includes a controller and an outflow valve. The controller is adapted to receive a signal representative of an aircraft cruise altitude and is operable, in response thereto, to supply valve command signals. The outflow valve is coupled to receive the valve command signals from the controller and is operable, in response thereto, to selectively move between an open and a closed position. The supplied-valve command signals selectively move the outflow valve between the open and closed positions to thereby control aircraft cabin altitude rate of change magnitude to at least one of a first and a second substantially constant value until the aircraft cruise altitude is attained.
In yet another exemplary embodiment, an aircraft cabin pressure control system includes an input signal processor and a rate control processor. The input signal processor is adapted to receive a signal representative of an aircraft""s cruise altitude and is operable, in response thereto, to supply a signal representative of target cabin altitude. The target cabin altitude corresponds to a desired cabin altitude when the aircraft has ascended to the cruise altitude. The rate control processor is coupled to receive the target cabin altitude signal and is operable, in response thereto, to supply valve command signals that will selectively move an outflow control valve between an open position and a closed position to thereby control aircraft cabin altitude rate of change magnitude to at least one of a first and a second substantially constant value until the target cabin cruise altitude is attained.
Other independent features and advantages of the preferred cabin pressure control system and method will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.